This invention relates to a fractionation tray for use within a distillation column. It particularly pertains to a novel apparatus and apparatus to minimize the time and cost needed for assembling fractionation trays for use in distillation columns and other related devices in the separation between two or more fluids such as a vapor and a liquid.
Distillation is a method in which a process fluid, typically a vapor and a liquid mixture of two or more substances, is separated into its component fractions of a desired purity, by the application and removal of heat under high pressure or vacuum. Distillation columns are designed to achieve this separation efficiently.
Basic distillation begins from a top portion of a column to a bottom portion of the column. Heavier process liquid flows down the column while lighter process vapor ascends up the column. The main components of distillation columns include a vertical shell and column internals, such as fractionation trays or packings where the separation of the process vapor and liquid substances occurs. These column internals increase and enhance the separation between the process vapor and liquid. The internal configurations of the column internals such as tray spacing, column diameter, placement of assemblies to enhance flow increase the efficiency and thereby lead to a lesser requirement of energy.
In a typical distillation column, the fractionation trays are horizontally mounted within the vertical shell. The particular design of the fractionation tray facilitates and enhances the separation between the process vapor and liquid by providing a more intimate contact between the fluids which leads to better separation. Each fractionation tray is comprised of several panels which are typically bolted to each other and subsequently attached by bolting or clamping to a cross-beam support member in the distillation column. The region between each panel and the support member is a "dead-zone" where little or no vapor-liquid interaction and separation occurs.
The area of the fractionation tray where the vapor and liquid contact is typically called the active area. The dead-zone regions or area between panels and surrounding the support member is generally subtracted from this area as an inactive area and does not contribute to the separation process. Thus, the combination of the dead-zone regions of all the fractionation trays reduces the efficiency of the column and more trays are required to balance the effect.
Recently, U.S. Pat. No. 5,468,425 to Nutter discloses an apparatus for modifying the dead-zone area of the trays to address the vapor-liquid contact in this area. The substantially large overlapping margin areas between the adjacent panels are provided with substantially geometrically identical apertures between each panel. The large margin areas are required for attaching the adjacent panels together by bolting.
While the addition of apertures in the margin area provides more apertures, the conventional bolts contribute to the same dead-zone problem as in conventional fractionation tray panel designs. Since the overlapping margin areas are significant and run the length of each adjacent panel, the area needed by the bolts to attach each panel together contributes to the dead-zone area. Thus, the benefit of apertures in the margin region are reduced in the capacity and efficiency of the tray and column.
Additionally, the Nutter tray follows conventional tray designs with respect to the installation of such trays by requiring two or more installers. Since each panels is attached to an adjacent panel by a bolt, at least one installer above the tray needs to position and align the bolt hole in one panel with the bolt hole in the second panel. Additionally, an installer must be positioned below the tray to ensure final bolting with either a nut or other locking device. A person skilled in the art will recognize that this conventional installation procedure is a substantial labor cost during the installation of the fractionation tray and contributes to the increased time required for the installation of the distillation column. Thus, there are no labor costs or time savings when required such as during a revamp whereby the entire plant is shut down to accommodate the replacement of the tower internals and any additional non-operational time impacts on the operation of the plant.
Accordingly, there is a need for a fractionation tray which reduces the dead-zone regions between the fractionation tray panels to provide an additional increase in the column capacity and efficiency. The fractionation trays should be easy and simple to construct while retaining enough strength for use in the high pressure vapor and liquid environment. The fractionation tray should also be easy to install to substantially reduce the labor cost and provide time savings during critical installations.